Process and means for measuring soil resistivity and certain electrical characteristics associated with a buried pipe line



2,378,440 unme SOIL RESISTIVITY AND CERTAIN ELECTRICAL CHARACTERISTICS ASSOCIATED WITH BURIED PIPELINES June '19; 1945." G. N. SCOTT PROCESS AND MEANS FOR MEAS v 5 Sheets-Sheet 1' Filed Jan. 27, 1941 1 [NYE/V702 60200 A. 5 co 7'7 Wfiw n my 1 Afraellsv.

' June 19,- 1945.

. I G. N. SCOTT PROCESS AND MEANS FOR MEASURING SOIL RESISTIVITY A ELECTRICAL CHARACTERISTICS ASSOCIATED WITI- I BURIED PIPELINES 5 Sheets-Sheet 2 llalll Filed Jan. 27, 1941 M Wm. M 5M wmm Mn 0 Y. Z a a June 19,1945. A s. N. sco'r'r 2,378, 0

MEANS FOR MEASURING.-SOIL RESISTIVITY AND CERTAIN ED PIPELINES PROCESS AND ELECTRICAL CHARACTERISTICS ASSOCIATED WITH BURI I Filed Jan. 27, 1941 5 Sheets-Sheet 3 IA'VE/YTOE 6020 0. A. 50077 June 19,1945. Q G. N. soso'r'r 2,378, 0

PROCESS AND MEANS FOR'MEASURING SOIL RESISTIVITY AND CERTAIN ELECTRICAL CHARACTERISTICS ASSOCIATED WITH BURIED PIPELINES 'Filed Jan. 27,. 1941 5 Sheets-Sheet 4 Y IZYVE/YTOR:

60 900 A. Scam BY 4% M. M MM June 19,1945. 6. N. SCOTT- 7 2,378,440

PROCESS AND MEANS FOR MEASURING SOIL RESISTIVITY AND CERTAIN ELECTRICAL CHARACTERISTICS ASSOCIATED WITH BURIED PIPELINES Filed Jan. 27, 1941 5 Sheets-Sheet 5 A 60200 /X Scarf,

ATTOR/YEK Patented June 19, 1945 PA'lENT OFFICE lpnooass AND MEANS FOR MEASURING SOIL A I 'RESISTIVITY ANDI CERTAIN ELECTRICAL cunmcrrnmsnos ASSOCIATED WITH A BURIED PIPE LINE r v ittGordon N. Scott, Beverly Hills, Calif. Application January 27, 1941 Scria1No. .376,134 '15 Claims. (c1.175 1ss') in n on relates broadly to a p ocessand mea s I r obtaining measurements p rtai n to buried, pipelines andparticularly-to methods and means for securing complete records thereof.-

7 I Ina process f determining the corrosive quality of soil along a rightsof way, for locating cor.- roded pipe and for studying the efiects ofthe electrical process of cathodic protection, a m-uItitude of measurements must be made. Heretofore practice consisted .of .In-aking Jsuch measurements over the rightr-iofewaysat long intervals det rmined in part by. the demands of economy. Such prior practice is'ha hazard, slow, tedious and, expensive and yield results which are both inaccurate and misleading, and may in. m instances .be'of no significancejowing to the lack of intermediate values in'm esurement. in-

ent non the contrary p rmits continuous and simultaneous measurement of d rd ng of a variety of quantities a'ndeliminates all of the lfqrementioned disadvantages and objections. "Furth rmore, iii-certain embodiments of my inention, n vel me surable quantities obtained by certain novel geometri al arrangements, ar made useful by my invention. I r ,An object of my invention. is to provide a procs. andmeans f r measu ings bstant a y continuously one or more characteristics of the, soil as the r s stivity, eith r sin ly r tog t Withcerta n. other electri al characteristics assoiat dwith a pe ne suc s e potential the pipe with reference to an'electrode in con-- ta t with adjac nt r emote s il, t s n an magnitude o radial ar-thcurren s, t ep t ti l eradiw thro e'h t e o l over-th pipe and the drop in potential through a coating caused by interrupted xternal'sour e f cu t cha gedbetweeri ar mote pointin' t e soil and I the pipeline.

Another o jector m finvention is to pr vid a vprocess and for measurin over an elected path without material excavation and substantial y con in ou ly a pr perty of h il elated toitscorrosiv qualityr I Y s Another object of my invention is to provide I aprocessfand means for measuring substantially continuously the soil resistivity in an'open trench in which a pipeline isto be laid. I I .I Another obj ct of my in nti n is to provide a non-polarizing electrode which is adapted to be moved continu usly al n the. ground and whi h is adapted to be in good electrical contact with the soil over the entire distance ver which it is moved. I I j I Another object of my invention is to provide a process'and means for measuring substantially continuously the potential of a buried pipeline with reference to a moving electrode in contact with the soil and preferably in which the radial geometric relation of the moving electrode is substantially fixed with relation to the longitudinal axi of the pipeline.

Another object of my invention is to provide a process-and means for measuring substantially continuously the potentials of a plurality of buried parallel and adjacent pipelines with ref- .erence to a moving electrode in contact with the soil.

Another object of my invention is to provide a process and means for measuring substantially continuously the potential gradients in the soil either alone orzin relation to a buried pipeline and preferably in some fixed geometrical relation with the pipeline. I I I Another object of my-invention is to provide a process and means for measuring substantially continuously and substantially simultaneously the potential gradients in the soil lying in a moving plane perpendicular to the axis of a buried pipeline in which the electrode in the moving plane bear a constant geometric relation to the intersection of the axis of the pipeline with the moving plane and preferably lying in a moving plane perpendicular to the axis of aburied pipeline wherein an electrode in the plane lies substantially verticallyover the axis of the pipeline.

Another object of my invention is to provide a process and means for measuringsubstantially continuously and substantially simultaneously the potential gradients in the earth surface'lying in a movingplaneperpendicular to the axis of a buried pipeline in which an electrode in the plane lies substantially vertically over the axis of the axis of the pipeline that the potential gradient IIt-herein is numerically equal to the gradients taken laterally in order that from said plurality of instantaneously associated measurements, the potential of 'thepipeline exclusive of soil gradientsimay be determined.

A furtherimportant object of my invention is to provide a process and means for measuring substantially continuously and substantially simultaneously the relativity of the soil and the potential gradients in the soil on either side of a point immediately over a buried pipeline so that from the associated measurements of resistivity and potential gradients the approximate density of the current entering or leaving the pipeline radially through the soil may be determined.

Another object of my invention is to provide a process and means for measuring substantially continuously and substantially simultaneously the potential of a pipeline with reference to a moving electrode in contact with the soil, the potential gradients in the soil and the resistivity of the soil.

Another object of my invention is to provide a process and means for measuring substantially continuously and substantially simultaneously in conjunction with an external source of current discharged to the pipeline from a point in the soil and in further conjunction with means intermittently to interrupt the current, the potentials of a coated pipeline with reference to a moving electrode at the particular point in the soil over the pipe, and the soil gradients in the soil laterally displaced from the said center point in the two instances of applied and interrupted soil currents whereby from said plurality of associated measurements may be determined the effect of cathodic polarization on the pipeline'and the drop in potential through the coating due solely to the imposed soil currents.

Another object of my invention is to provide a process and means for measuring substantially continuously and substantially simultaneously in conjunction with an external source of current discharged to the pipeline from a point in the soil and in further conjunction with means intermittently to interrupt the current, the resistivity of the soil, the potentials of a coated pipeline with reference to an electrode at a point in the soil over the pipe, and the soil gradients in the soil laterally displaced from the said center point in the two instances of applied and interrupted soil currents whereby from said plurality of associated measurements may be determined the effect of cathodic polarization on the pipeline, the drop in potential through the coating, the average current which enters the pipe radially and which is due solely to the imposed soil currents, and the conductance of the coating.

Another object of my invention is to provide a process and means whereby all of the foregoing substantially continuous measurements and combinations of measurements may be singly and in combination recorded substantiallycontinuously and substantially simultaneously and preferably in units of distance whereby such continuous records are related in point to point correspondence with the distance from a fixed point in space measured by the progress of the vehicle upon which are mounted the means for applying the invention.

By the term substantially continuously it is meant that the measurements are recorded on the chart in regular linear intervals, however small, arbitrarily fixed within limits by the characteristics of the meters and markers of the recorders.

By the term substantially simultaneously it is meant that two or more measurements are recorded on a chart in regular linear intervals either truly simultaneously or staggeredly wherein the latter case a single meter in place of two or more may be adapted to one recorder alternately and regularly to record the several measurements.

My invention has many other objects, advantages, and features, some of which, with the foregoing, will be set forth in the following description where I shall outline certain forms of my invention which I have selected for illustration in the drawings accompanying and forming a part of the present specification.

Referring to the drawings:

Figure lis a top view of a device the features of my invention.

Figure 2 is a side view of the device shown in Figure 1.

Figure 3 is a schematic drawing showing the details of the recorder drive mechanism.

Figure 4 is a view, partly in section, of the non-polarizing electrode assembly.

Figure 5 is a section of the portion of the non-polarizing electrode adapted to contact the soil.

Figure 6 is a schematic drawing of the electrical circuits of the device shown in Figure 1.

Figure 7 is a schematic drawing of electrical circuits adapted to be used in conjunction with the electrical circuits shown in Figure 6 in a modification of my invention.

Figure 8 is a rear view of a modification of my invention for measuring the resistivity of the soil in an open trench.

Figure 9 is a fragmentary side view of the modification shown in Figure 8 showing one means to raise and lower the electrode assembly in and out of an open trench.

Referring to Figures 1 and 2 of the drawings, the numeral l0 indicates the frame of a vehicle which may be either externally or self-propelled, forexample, the frame of a conventional tractor. Means are mounted on the frame l0 to provide a embodying substantially continuous record of the resistivity of the soil over which the vehicle is moving irre spective of the presence or absence of pipelines. As an instance of this arrangement, the frame II] is provided with an insulated support II. A plurality of electrodes 12 are adjustably mounted on the support ll by'means of sleeves I3, rods I4, spring arms [5, so that the electrodes l2 can rise over any obstructions that the electrodes might engage and so that the electrodes are forced into intimate contact with the soil. The electrodes l2 may be formed of suitable steel members and the lower ends may be in the form of a plow in order to cut a shallow furrow in the soil to the desired depth in order to provide a good electrical contact with the soil.

In order to raise and lower the electrodes l2, a rod I6 is connected to the support I l and a lever I! is provided to move the rod (6 and thereby raise or lower the electrodes I2.

The outer two of the electrodes l2 are wired to a constant current oscillator (not shown), carried in the oscillator compartment 20 which is attached to the supports 2| carrying the meters. The inner electrodes I2 are wired to a recording meter.

Means are-provided so that one or more, and preferably all of the recording meters are operated synchronously with the vehicle, without reference to time. As an instance of this arrangement and as shown in Figure 3, the recording meters are operated by means of flexible shafts 23 which are attached to a set of reducing gears 24 in the gear box 25. The gears 24 in the gear box 25 are caused to turn by the flexible shaft 26 which is geared to a gear 21 on the wheel axle 28 within the axle housing 29.

Means are also mounted on the frame ID to provide s, substantially continuous recordof certaln electrical characteristics of the: plpelineand to insure goodelectrical contacts of theelectrodes/ with the soil; 'In order to raise-and lower the electrodes 3|, a rod 36 is connected to the support and a, lever 31 is provided to moveth'e rod 36, and thereby raise and lower theelectrodes 8| Referring to Figures 4 and '5, I show one form of a nonpolarizing electrode which is suitable for use in connection with my invention. Mounted in the vehicle and insulated therefrom .are a plurali'ty of copper containers 40 which are closed by wide mouth copper caps 4| which are provided with bailles 42 and air vents 43. Also provided on the containers 4!! are electrical'terminals 44 of copper. Within the containers are crystals of copper'sulphate 45 and saturated aqueous solutions thereof. Also within the containers and extending through them are copper tubes 46 adapted to permit the passage of only saturated copper" sulphate solution through 41 to the electrodes 3|. 3 e I Referring to Figure 5 the copper sulphate electrode 3| may be composed of a cylinder 51L formed of non-metallic materiaL'su'ch as Lucite or wood. The lower end of the cylinder 5|! is preferably flattened to contact the soil in the bottom of the furrow cut by the plow 35. Small holes 5| are provided on the trailing section 52 and the bottom portion 53 of the cylinder 50. Theholes 5| are drilled on the bottom surface 53 parallel to the axis of the cylinder 56 and parallel to the ground surface on the trailing edge 52. The holes- 5| are designed to prevent clogging by the soil and to provide seepage of the copper sulphate solution to insure electrical contact of the 'soil with the solution within the containers-40. The cylinder 53 is closed by a threaded cap 54 having a fluted extension 55 for sealing engagement with the rubber hose 41.

Reels 56 of insulated wire are mounted onthe support '51. The reels are adapted to provide many hundred feet of insulated wire for a purpose to be described hereinafter.

is caused to pass between the outer electrodes. An 6 instance of this arrangement is shown in Figure 6 in which a source 59 of alternating current of constant Strength is caused to pass between the outer electrodes l2 by means of lead wires 60 and 6| and in'which the alternating potential developed between the inner pair of elctrodes i2 is rectified'and measured on the recording meter 62. As the vehicle is moved over the ground, a record 63 of the resistivity of the soil is obtained, said record beingin. point of distance without the rubber hoses v reference to time in that, therecorder is synchronized with the movement-of the vehicle. v

i The potential of a pipeline may be'measured withrespect-to'any point the soil, and a substantially continuous record of said potentials may beobtained by maintaining as the vehicle moves a constant radial geometric relation of an electrode with respect'to the axis of the pipeline. Referring to Figure 6, in which the use of three non-polarizing electrodes 3| is indicated, means are shown for measuring the potential of the center electrode 3| over the, pipe 64. The pipe 64 is connected to a, recording voltmeter 65 by means of insulated wire 66 from one of the reels 56. The center electrode 3| is connected to .said voltmeter/65 and tothe terminal 44 of the copper container 40 by means of insulated wire, '61. In the circuit are provided chokes '68 and 69, and a condenser ID to eliminate the effects of alternating currents. ,As thevehicle is moved over the surface of the ground, the plow 35 cuts a shallow furrow in the soil in which "the center electrode 3|-is adapted to follow. A small amount of copper sulphate solution is adapted to seep through the small holes 5| in order to insure contact of the soil with the solution'in the container 40. face of the ground in constant geometric relation with respect to the pipeline 64, a record TI is obtained of the variations in potential of the pipeline 64 with respect to the center electrode 3| in I contact with the soil. As shown in Figure 6, for reasons which will be made evident hereinafter; Iprefer to have'the center electrode 3| in contact with the soil directly above the pipeline 64, although in other applications of my invention, Iplace an electrode 3| at other geometrical configurations with respect to the pipeline 64;

The sign and magnitude of the potential in the earth surface on a sectionof soil betweenpoints over the pipeline and laterally displaced therefrom serves to indicate whether the pipelineis picking up or discharging current which data gives important information on the condition of the pipe with'respect to corrosion as well as other useful information.

Since relative magnitude and the signs of the potential gradients may be different on each side of the pipeline it is advisable to measure both potential differences of the outer electrodes with respect to the central electrode 3|.

The recording meter 12 contains two milli voltmeters, the common terminal of which is connected to the central copper sulphate electrode 3| through the lead wire 61. The outer electrode 3| are connected through the terminals 44 of the copper containers 40 and the lead wires 13 to'the appropriate terminalsof said recording meter 12. Chokes 14 and condensers 15 are provided, to eliminate'the-effects of alternating currents. As the vehicle is moved over the surface of the ground a-record 16 isobtained of the difference in potential of the. center-electrode with respect xtoone of the outer electrodes and a record 11 is obtained of the difference in potential of the center'electrode with respect tothe other outer electrode, said records being in point with the movement of the vehicle.

When the electrode 3| spacing :1: bears the hereinafter fixed relation with the quantity h s which is the sum of the depth of the soil above the pipeline and the pipeline radius a, thenthe average of the readings at that particular point the vehicle is moved over the sur- .rectifier 8| through a resistance 90.

on.ithe records I6 and I1, Ave, is numerically equal to the difference in potential existing in the soil between the center electrode and the pipe surface. In other words the records I6 and 11 indicate the differences in potential in, or the ir drop through the soil between the center electrode and the pipe surface when the geometrical factors bear the following relation:

' h(ha) It is obvious that the record II may be corrected by the use of the records 16 and 11 since the potential of the pipe as indicated by the record II contains the average of the potentials of records 16 and I1 existing between the center electrode and the pipe surface.

Furthermore, providing that the size of the pipe is fixed, that the depth of the soil above the pipe is reasonably constant, and that the records 63, I6 and l! have been taken substantially simultaneously, the density of the current entering or leaving the pipe may be calculated from the relation 'KA V, Current densitym in which K is a constant of logarithmic form in which are as variables the quantities a, h, and .r and in which Ave is the average difference in potential measured in the soil between the center electrode and the outer electrodes.

If in the particular measurements sought the z'r drop through the soil is of negligible importance in comparison to the magnitude of the radial currents then clearly by suitable electrode spacing the value of the constant K may be so fixed in round numbers as greatly to facilitate subsequent use of the records.

In Figure 7, in which are schematically illustrated embodiments of a modification of my invention adapted to be used in conjunction with the electrical circuits shown in Figure 6, is shown a typical cathodic protection installation to which has been adapted means for intermittently interrupting the cathodic current. One instance of this arrangement is as follows:

In the modified cathodic protection installation illustrated are shown the pipeline 64, an externally placed anode 80, a rectifier 8I, coupled through a, transformer 82 to a source of alternating current. The positive terminal 83 of the rectifier is connected to the anode 80. The negative terminal 84-of the rectifier is connected to a common terminal 85 of a magnetically operated mercury switch 86, one terminal 81 of which is connected to the pipeline 64. The other terminal 88 of the magnetically operated switch 86 is connected to the positive terminal of the The solenoid 9| of switch 85 is energized by a small portion of the rectifier current which is caused to pass through the variable resistance 93 and a polarity changer 94 diagrammatically shown in Figure '7 as connected to one position of polarity. The operation of the polarity changer by a conventional time clock (not shown) is such as to cause the solenoid leads alternately to connect to the fixed polarities of the rectifier leads. The change in polarity of the solenoid 9I is such as to intermittently open and close the terminals 81 and 88 of the switch 06. The resistance 90 is approximately equal to the overall resistance of the anode 80 and the pipeline 64. In this way, the output of the rectifier is maintained substanmounted on the frame I0.

tially constant while due to the action of the switch 86, the current is intermittently diverted from the soil through the resistance 90.

In the operation of this modification, two records are obtained on the recording meter 65, one of which records is a record of the potential of the pipe with reference to the center electrode while the current through the soil from the rectifier is interrupted, and the other record is a record of the potential of the pipe 64 with reference to the center electrode while the current from the rectifier is passing through the soil to the pipe. Similarly four records or curves are obtained on the recording meter I2, one pair of which is a record of the potential gradients in the soil while the current through the soil from the rectifier is interrupted and the other pair of which is a record of the potential gradients in the soil while the current is passing through the soil to the pipeline 64.

As the vehicle moves over the surface of the ground, substantially continuous records are made.

Considering a pair of the records or curves on the recordingmeter 12 obtained from the central electrodes 3i and one of the outer electrodes 3|, it is apparent that the difference of potential (AZ'ViD) at any point in the records or curves is due solely to the interrupted current from the rectifier and that the average of this value of Alva: and the similar value from the central electrode and the other outer electrode together with the measured resistivity of the soil provides the information from which can be calculated the average radial current density due to the rectifier current in the soil alone in accordance with the formula set forth on line 26 supra.

Further, said average value of AiVI is approximately equal numerically to the drop in potential between the central electrode and the surface of the pipeline 54, or of the outer surface of the coating if the pipe is coated, caused solely by the rectifier current in the soil.

Similarly, considering the pair of records or curves obtained on the recording meter 65 it is evident that the difference in potential between the two curves at any particular point measures the drop in potential through the soil from the central electrode to the surface of the pipe, or to the outer surface of the coating if the pipe is coated, and the drop through said coating caused solely by the rectifier current in the soil. Accordingly, the resistance of the coating, if any, is readily calculated at any particular point in the curves from the difference in the values obtained from the records II of the recording meter 65 by subtracting therefrom the average of the values Alva: and dividing the result by the calculated density of the current in the soil due to the rectifier alone.

In the modification of my invention shown in Figure 8, I show a device adapted to measure the resistivity of the soil particularly in the lower portion of an open trench which is adapted to receive a pipeline. A rigid support I00 is The support I00 is provided with a fixed sleeve 10! which is adapted to be connected by'a rotary joint I02 to a support I03. The rotary joint I02 is adapted to permit the support I03 to be moved laterally in said joint and to rotate the support I03 by control means (not shown). An insulated frame I04 is suspended from the support I03 and braced by insulating cross members W5. A plurality of electrodes I06 are adjustably mounted on the acreage I051; ;b'yr means. of assemblies. I 01 comprising sleeves, rods, spring .arms tand springslto permit inoperation theiree andindependent movement of the several electrodes 16. Theelectrodes may be ffoImecL of. suitable steel -members, and. the lower ends may be in the .form of plows; in order tolcutl shallow furrows in the soil to the desired 'depth' so that good electrical contacts betwee I the electrodes and the soil are'assureds a tial difierences in, the earth developed by. the 'current discharged from theoscillatorw llw are measured between the bottom electrode I and oneoffthe lower horizontal electrodes lllfi and between the-bottom electrode and .theotherlower horizontal electrode I06, Since the bottom ,electrode common in each pair of. electrodesbetween which the potential is measured, variations in said measurement at any, particular point are attributable todifierences, in the soilimmediately surrounding the lower electrodes, ,v Providing both the strength of the current discharged from the upper electrodesgandthe geometrical relationship of; the substantially co--. planer electrodes remain unchanged, then it may be shown the resistivityot the soil is directly proportional to the measured valuesof the potenaldi ier c Y l Asthe vehicle ismoved over the'ground two,

' rec rQs IlM fthe resistivity of the soil are ob-c tained, said records being in point of distance rather than with reference to time since the recorder is synchronized with the movement of the h l .v t

In Figure 9 are shown means to hold the frame members Ill-l in a vertical-position in the trench and to rotate the said frame out of the trench. In more detail the frame member I0 is con:

- nected to a cord I which passes over the pulley I |2|. The pulley l2l, is connected by means of the hooksl22 and the spring I23 to the cord I24 whichis passed over the wheel I25 affixed to the frame 10 to the drum l26- whichis' provided with the crank T27. I

Itv willrbe' apparent that my invention is adapted to be used in connection with the exploration of plots of ground for the purpose of most advantageously placing anodes foicathodic p rotection in ,thatv the final resistance of the the soil resistivity: my invention is otparticular utility. 1 J $1.91: Y thematterof applications my device may be :used' to securerecords .from which maybe drawn. the equipotential contours and. the like over an area within which lie two or-more pipee lines for. the purpose of studying the effects of cathodic protectionapp t h e p p for. instance, onivtheothers. v 1 Furthermore, the effectrot one of two parallel pipelines upon thelotherx maybe studied by my invention using four electrodes in particularsubstantially collinear arrangement; For instance the continuous: and simultaneous records of the surface earth gradients on the outside of of the pipelines: would indicate'whether an exchange of current was occurringin that-it maybe shown, gradientsof like sign would indicate current exchange and also the pipeline polarities and .in thatgradients'of. unlike sign would-indicate simultaneous: pick up tor-discharge of current. Furthermore, additional simultaneous records of the individual pipe potentials with reference to their adjacent electrodes would greatly addoto the value of the first mentioned records :in vthat the records would also tend to anode, lower inthe lower resistance soils ,gin part determines the consumption of power. a

Similarly in some systems of cathodicprotection a multiplicity of small. distributed anodes are laid in preference to the customary widely separated installations, In such instances not only is the location of low resistance ground im-' portantfor the anodes but also the location of the anodes in? opposition to the pipeline in regions where current enters the soil from the I pipeline leads to most advantageous distribution o'ftheimposed currents and in these measurements, or the soil, gradients about a pipeline and tinuously show the polarity. of the pipe withreference to thesoil.n l

From the.foregoingndescription taken in con nection c with the accompanying I drawings, the uses, advantages, and operation of my invention will be readily understood by those skilled in the art to which the invention .appertains. awhile I,

have described the principle of operation'to- 'gether with the forms of my invention which I now consider, to be the best emboclimentthereof, Idesire to'h'aveit understood that the articles shown are merely illustrative and that the invention is .notto be limited to. the details :disclosed herein, but is to be accorded the full scope of the appended claims. I

I claim: 1

1. A process of substantially continuously-and substantially simultaneously measuring the potential gradients in the soil on both sides of the vertical plane through the axis'o-f. a. buried pipeline which comprises positioning a center electrode in saidvertical plane, electrically coning oneelectrode on each side ofsaid center electrode and in a plane perpendicularto said vertical plane and at such a distance from said center electrode which is that particular geometrical function of the shortest distancexfrom the center electrode to the longitudinalaxisof the pipelineso that the average of the measured 'gradients is approximately numerically equal to the earth gradient between said center electrode and said pipeline, connecting each of said last mentioned electrodes each to one of said meters, and moving saidelectrodesparallel to said pipe-. line'and in continuous electrical contact with the soil.

2. A process ofdetermining over a length of buried pipeline the potential of said pipeline with reference to a moving electrode in electrical contact with the soil exclusive of soil gradients by measuring the potential of the pipeline with reference to an electrode in electrical contact with the soil and subtracting therefrom the earth gradients between said electrode and said pipeline which comprises substantially conand substantially simultaneously measuring thepotential of said buried pipeline with reference to a non-polarizing electrode in electrical contact with the soil by positioning said electrode in a vertical plane through the axis of the buried pipeline and by positioning one electrode on each side of said plane at a distance from the center electrode and in a plane perpendicular to the axis of said pipeline and at such a distance from said center electrode which is that particular geometrical function of the shortest distance from the center electrode to the longitudinalaxis of the pipeline so thatlthe average of the measured gradients is approximately numerically equal to the earth gradient between said center electrode and said pipeline, by electrically connecting said first mentioned electrode with each of three meters, one of which meters is electrically connected to said pipeline, and by electrically connecting each of said last mentioned electrodes each to one of the two of said meters which aretnot connected to said pipeline, and moving said electrodes in continuous electrical contact with the coil and parallel to the pipeline.

3. A process of substantially continuously and substantially simultaneously measuring over a.

trodein electrical contact with the soil, the

potential gradients in the soil adjacentsaid pipeline and the resistivity of said soil in conjunction with an intermittently interrupted source of current discharged from a point in the soil to said pipeline, and determining from these factors the instantaneous value of the current densityat the point of measurement.

5. A device for obtaining a substantially continuous record of the resistivity of the soil over which the device is adapted to be moved comprising a vehicle, a plurality of electrodes in fixed separation mounted'on and insulated'from said vehicle, said electrodes being adaptedfor continuous movement over the surface of the soil and to makecontinu J ous electrical contact with the soil, certain of said electrodes being connected to a source of current, and a recording meter connected to others of said electrodes, said recording meter being mounted on said vehicle and the chart of said recordingmeter being adapted to be moved in direct proportion to the forward movement of said vehicle.

6. A device for obtaining a substantiallycontinuous record of the resistivity of the soil about a buried pipeline over which the device i adapted to be moved comprising a vehicle, a plurality of substantially collinear equally spaced electrodes mounted on and insulated from said vehicle, said electrodes being adapted to make a shallow furrow in the surface of the soil as the vehicle is moved in order to insure continuous electrical contacts of said electrodes with said soil, said electrodes being spaced in such relation as to provide readings of the resistivity of the soil to substantially the depth of said pipeline, certain of said electrodes being connected to a source of current and others of said electrodes being'connected to a recording meter.

7. A device for obtaining a substantially con tinuous record of the potential of a length of buried pipeline with reference to a moving'nonpolarizing electrode in contact with the soil comprising a vehicle having mounted thereon means to make a shallow furrow as the vehicle is moved, a non-polarizing electrode, a recording meter and a length of insulated wire, said electrode being adapted to electrically contact the soil in said furrow and electrically connected to said meter, and said pipeline being connected to said meter by said insulated wire.

8. A device for obtaining a substantially continuous record of the potential gradients in the soil above a buried pipeline, over which the. device is adapted to be moved comprising a vehicle, a plurality of substantially collinear electrodes, and recording meters mounted on said vehicle, said electrodes being adaptedto make continuous electrical contact with the soil as the vehicle is moved over said soil, the center electrode being electrically connected to both of said meters, and the outer electrodes being connected one to each of said meters.

9. A device for obtaining asubstantially continuous record of the potential gradients in the soil adjacent a buried pipeline over which the device is adapted to be moved comprising a vehicle, a plurality of substantially collinear electrodes and meters mounted on said vehicle, said electrodes being adapted to make continuous electrical contact with the soil and spaced in such relation that the average difierence in potential between the center electrode and the outer electrodes is substantially the same as the difference in potentialbetween the center electrode and the surface of said pipeline, the center electrode being electrically connected to both of said meters and the outer electrodes being connected'one to each of saidmeters.

10. A device including a vehicle for obtaining substantially continuous and substantially simultaneous records of the resistivity of the soil about a buried pipeline over which the vehicle is adapted to be moved, of the potential of said pipeline with reference to a non-polarizingelectrode in electrical contact with said soil, of the change in said potential caused by an interrupted external source of current discharged into the soil from a point in the soil to the pipeline, of the potential gradients in the soil adjacent said pipeline and ofthe changes in said gradients caused by the interruption of said external current which comprises a large electrode in the soil remote from said pipeline and electrically connected to a source of direct current, said source of direct current being electrically connected to said pipeline, means for intermittently interrupting said current,'said vehicle having a-plurality of collinear equally spaced electrodes mounted on and insulated from said vehicle, said electrodes being spaced in such relation as to provide records of the resistivity of the soil to substantially the depth of said pipeline, certain of said electrodes being connected to a source of alternating current and others of said electrodes being connected to a recording meter, a plurality of'substantially collinear non-polarizing electrodes each insulated from each other and from said vehicle and three meters provided with alternating current chokes and by-pass condensers all mounted on said vehicle, said nonpolarizing electrodes being adapted to make continuous contact with the soil and spaced in such relation that the average difierence in potential between the center electrode and the outer nonpolarizing electrodes is substantially the same as the difierence in potential between the center non-polarizing electrode and the surface of said pipeline, said center non-polarizing electrode being electrically connected to all three of said lastmentioned meters, and the other of said nonpolarizing electrodes being connected one to each of two of said last-mentioned meters, the third of said last-mentioned meters being electrically connected to said nineline. i

11. A device for obtaining substantially continuous measurements of an electrical characteristic of an energized soil over which the device is adapted to be moved comprising a vehicle, a plurality of. relatively fixed electrodes mounted on and insulated from said vehicle, said fixed electrodes being adapted for continuous movement over the surface of the soil and to make'contin- I uous electrical coupling with said energized soil, and a meter carried by said vehicle and connected 7 to said electrodes.

12. A device for obtaining substantially continuous measurements of an electrical characteristic associated with an energized underground pipe line over which the device is adapted to be moved comprising a vehicle, a plurality of relatively fixed electrodes responsive to energization mounted on and insulated from said vehicle, said fixed electrodes being adapted for continuous movement over the surface of the soil and to I make continuous electrical coupling with said enfrom said vehicle, said electrodes being spaced in such relation as to provide readings of the average resistivity of the soil to the order of the depth of said pipeline, certain of said electrodes bein connected to said source of current and others of said electrodes being connected to said recording meter.

14. A device for obtaining a substantially continuous record coordinated with distance but independent of time, of the electrical characteristics of the soil over which the device is adapted to be moved, comprising a vehicle, a plurality of electrodes mounted on and insulated from said vehicle, said electrodes being constructed and arranged to make continuous electrical contact with the soil, a source of current, means for connecting said source to certain of said electrodes, a recording meter carried by said vehicle, and including a chart, and means for causing said chart to move through a distance directly proportional to the distance of forward movement of said vehicle;

15. A device for obtaining a substantially continuous record of an electrical characteristic of an energized soil over which the device is adapted to be moved comprising a vehicle, a plurality of electrodes in fixed separation mounted on and in- I sulatedfrom said vehicle, said electrodes being adapted for continuous movement over the surface of the-soil and to make continuous electri cal contact with the soil, and a recording meter 

